As compared to conventional tissue removal techniques, electrosurgical procedures are advantageous in that they generally reduce patient bleeding and trauma. More recently, electro surgical devices have gained significant popularity due to their ability to accomplish outcomes with reduced patient pain and accelerated return of the patient to normal activities. Such instruments are electrically energized, typically using an RF generator operating at a frequency between 100 kHz to over 4 MHz.
Many types of electrosurgical devices are currently in use. They can be divided to two general categories—monopolar devices and bipolar devices. When monopolar electrosurgical devices are used, the RF current generally flows from an exposed active electrode, through the patient's body, to a passive, return current electrode that is externally attached to a suitable location on the patient body. In this manner, the patient's body becomes part of the return current circuit. In the context of bipolar electrosurgical devices, both the active and the return current electrodes are exposed, and are typically positioned in close proximity to each other (normally mounted on the same instrument). In bipolar procedures, the RF current flows from the active electrode to the return electrode through the nearby tissue and conductive fluids.
High frequency electrosurgical instruments, both monopolar and bipolar, have been used in the context of many surgical procedures in such fields as urology, gynecology, laparoscopy, general surgery, arthroscopy, ear nose and throat and more. In many fields of electrosurgery, monopolar and bipolar instruments operate according to the same principles. For example, the electrosurgical interventional instrument, whether monopolar or bipolar, may be introduced through an instrument such as a resectoscope, or alternatively directly to perform the needed surgical procedure in the target area of the patient's body. In some cases, an externally supplied liquid (often referred to as an “irrigant”), either electrically conductive or non-conductive, is applied. In other electrosurgical procedures, the instruments rely only on locally available bodily fluids, without requiring an external source of fluid. Procedures performed in this manner are often referred to as performed in “dry-field”. When necessary, the electrosurgical instruments may be equipped with irrigation, aspiration or both.
Even though the benefits are well recognized, current electrosurgical instruments and procedures suffer from very significant deficiencies. For example, monopolar devices require the use of an additional external component, namely one or more grounding plates, remotely attached to a suitable location on the skin of the patient. Thus, in that monopolar devices require current to flow from the active electrode through the patient's body, they invariably allow for the possibility that some of the current will flow through undefined paths in the patient's body, particularly when the instrument is not properly designed and positioned.
Bipolar electrosurgical devices have their own inherent drawbacks, often resulting from the close orientation of the return and active electrodes. The return electrode necessarily has a small area and, as a result, can cause undesired tissue heating, coagulating or evaporation at its contact point with the patient's tissue due to the relatively high current densities present thereon. In addition, with the bipolar configuration, the close proximity of the active and return electrodes creates the danger that the current will short across the electrodes. For this reason, bipolar devices normally operate at relatively low voltage (typically 100 to 500 V) to decrease the chances that a spark will bridge the gap between the active and return electrodes.
Electrosurgical procedures which cut or vaporize tissue rely on generation of sparks in the vicinity of the active electrodes to vaporize the tissue. Sparking is often referred to as “arcing” within gaseous bubbles in liquid, or alternatively as plasmas. Operation at relatively low voltage, as is necessary with bipolar instruments, can lead to less efficient sparking, reduced efficiency of the instrument, undesirable overheating of nearby tissue, and longer procedure time. Moreover, the use of electrosurgical bipolar procedures in electrically conductive environments is inherently problematic. For example, many arthroscopic procedures require flushing of the region to be treated with saline, both to maintain an isotonic environment, to carry away process heat and debris, and to keep the field of view clear. The presence of saline, which is a highly conductive electrolyte, can also cause electrical shorting of a bipolar electrosurgical probe, thereby causing probe destruction and unintended and unnecessary heating in the treatment environment which, in turn, can result in unintended and uncontrolled tissue destruction.
In addition, current monopolar and bipolar instruments used to cut or vaporize tissue often do not have effective means for controlling bubbles, which is essential to the safety and efficiency of many procedures. As a result, the efficiency of the instruments is often low and the procedure length is increased. Electro surgical instruments that lack an effective means for trapping of bubbles include, for example, cutting loops, rollers, needles and knives, resection instruments and ablators. Furthermore, many current monopolar and bipolar instruments are not designed to take full advantage of either the electrical properties of the fluids present in the vicinity of the procedure site (bodily fluids, including blood, as well as irrigation fluids, either electrically conductive or non-conductive) or the electrical properties of the tissue itself.
Vaporizing electrodes (ablators) currently available for use in conductive liquids, whether monopolar or bipolar, have an active electrode surrounded by an insulator that is significantly larger in size than the ablating surface of the electrode. For ablators with a circular geometry, the diameter of the portion of the probe which generates ablative arcs (i.e., the “working” diameter) is generally not greater than 70 to 80 percent of the diameter of the insulator (i.e., the “physical” diameter). Accordingly, only about 50% of the physical probe area can be considered effective. This increases the size of the distal end of the electrode necessary to achieve a given ablative surface size, and necessitates the use of a cannula or other instrument, often with unnecessarily large lumens, an undesirable condition.
As noted above, it is well known in the prior art to use high frequency current in electrosurgical instruments, both monopolar and bipolar, introduced via an instrument such as a resectoscope, endoscope or directly, to perform the desired surgical procedure in such fields as urology, gynecology, laparoscopy, general surgery, arthroscopy, ear nose and throat and more. In fact, a number of radio frequency devices, both monopolar and bipolar, and techniques, both in conductive and non-conductive fluids, are described in the art for urological and gynecological purposes.
Endoscopic transurethral resection and/or thermal treatment of tissue is generally accomplished using a resectoscope, a device which allows the scope and other instruments to pass easily into the urethra. Resectoscopes are well known in the art. Various elongated probes are used to cut, vaporize, coagulate, or otherwise thermally treat tissue. For example, resectoscopes are often used in the treatment of benign pro static hyperplasia (BPH) or benign prostatic enlargement (BPE). BPH is a very common problem in western society and, if left untreated, can give rise to poor quality of life, urinary infection, bladder stones or even kidney failure. BPH is due to hormonal changes in the prostate and lifestyle of the patient, and is characterized by the enlargement or overgrowth of the gland as a result of an increase in the number of its constituent cells. BPH can raise PSA levels two to three times higher than normal. Men with increased PSA levels have a higher chance of developing prostate cancer. BPH usually affects the innermost part of the prostate first, and enlargement frequently results in a gradual squeezing of the urethra at the point where it runs through the prostate. The squeezing sometimes causes urinary problems, such as difficulty urinating. BPH may progress to the point of generating a dense capsule that blocks the flow of urine from the bladder, resulting in the inability to completely empty the bladder. Eventually, this can lead to bladder and kidney malfunction. Transurethral resection of the prostate (TURP) is the treatment of choice for BPH, and the most common surgery performed for the condition, using a resectoscope inserted through the urethra. Resectoscopes, along with their associated electrosurgical probes, are also used in various laparoscopic and gynecological procedures.
Endoscopic electro surgical probes of the type used with a resectoscope may be used with conductive or nonconductive irrigants. When conductive irrigants are used, current flows and/or arcing from any uninsulated portion of the active electrode which contacts the conductive fluid. Due to this reality, probes for use in conductive fluids must be insulated except for portions which will give the desired clinical effect during use. In a nonconductive fluid environment, conduction occurs only from portions of the active electrode which are in sufficiently close proximity to tissue to cause current flows and/or arcing between the electrode and the tissue, or from portions of the electrode which are in contact with tissue. During a surgical procedure, however, even non-conductive irrigants can achieve some level of conductivity, for example as a result of bodily fluids seeping from the patient's tissue into the irrigant. This contamination may increase the local conductivity to a degree sufficient to cause significant current flow from uninsulated portions of a probe designed for use in a non-conductive irrigant. Accordingly, it may be presumed that all fluids have some level of conductivity during laparoscopic electro surgery, and that all probes which are used partially or completely submerged in a liquid will benefit from a construction that maximizes electrode efficiency by maximizing the portion of the RF energy which provides clinical benefit.
Probes may be used for vaporization or for thermal modification, such as lesion formation. Vaporization occurs when the current density at the active electrode is sufficient to cause localized boiling of the fluid at the active electrode, and arcing within the bubbles formed. When the current density is insufficient to cause boiling, the tissue in proximity to the active electrode is exposed to high-temperature liquid and high current density. The temperature of the liquid and tissue is affected by the current density at the active electrode, and the flow of fluid in proximity to the electrode. The current density is determined by the probe design and by the power applied to the probe. Any given probe, therefore, can function as either a vaporizing probe or a thermal treatment probe, depending on the choice of the power applied to the probe. Lower powers will cause a probe to operate in a thermal treatment mode rather than in the vaporizing mode possible if higher power is applied.
The bubbles which form at the active electrode when a probe is used in vaporizing mode, form first in regions of the highest current density and lowest convection of the liquid. When they reach a critical size, these bubbles support arcing within and allow for vaporization of tissue. Bubbles also form in areas of lower current density as the conductive liquid in these regions reaches sufficient temperature. While these bubbles generally do not support arcing, they cover portions of the exposed electrode surface, thereby insulating these portions of the surface. This insulation of non-productive regions of the electrode decreases non-beneficial current flow into the liquid thereby allowing the electrode to achieve its clinically beneficial results at lower power levels. It is possible to increase electrode efficiency by managing these bubbles so as to retain them in regions in which their presence insulates the electrode.
In summary, the geometry, shape and materials used for the design and construction of electrosurgical instruments greatly affect the performance. Electrodes with inefficient designs will require substantially higher power levels than those with efficient designs. While currently available electrodes are capable of achieving desired surgical effects, they are not efficient for accomplishing these tasks and may result in undesired side effects to the patient.